Implantable medical devices (IMDs) used to monitor physiological conditions or to deliver therapy typically include one or more physiological sensors. Examples of IMDs include hemodynamic monitors, pacemakers, implantable cardioverter defibrillators (ICDs), myostimulators, neurological stimulators, drug delivery devices, insulin pumps, glucose monitors, etc. The physiological sensors used in conjunction with IMDs supply time-varying signals that are related to a physiological condition from which a patient's state or a need for therapy can be assessed.
Chronically implanted sensors function in an environment with changing artifact and signal characteristics, as well as serious power constraints. In order to provide the best therapy or diagnosis, it is important to identify, from the physiological signals produced by sensors, which signal or signals contains desired information regarding the physiological condition being monitored. It is also important to cancel or reduce the effects of artifacts within the sensor signals. This can be challenging in the use of chronically implanted physiological sensors, which can produce multiple sensor signals having differing signal responses under differing patient conditions.